His wife said he had seemed perfectly normal as he walked his children to the school bus at 0845, as he did every day.

However, when his wife returned to the family home around mid-morning she discovered suicide notes that he had written to each of his children.

The police said there were indications that he was motivated by an incident that happened some 20 years ago.

It is not thought that Roberts had anything against the Amish community but chose the school because it was close by and had young girls.

In a separate incident, two Las Vegas schools, one high school and one elementary school, were temporarily locked down while police hunted for a teenager spotted carrying a gun on the high school campus.

These latest incidents come at the end of a week of gun-related violence in US schools.

Last Wednesday a 16-year-old girl died when an armed man, who also killed himself, took six students hostage at a Colorado high school.

And on Friday, a head teacher at a high school in Wisconsin was killed when he confronted an armed 15-year-old student as he entered the school.